The prevalence rate of asthma in the general population appears to have increased substantially in recent years with a concomitant rise in gestational asthma. Recent data suggest that as many as 5% of pregnancies are complicated with asthma, and this appears particularly high in pregnancies of black (9%) and Hispanic (14%) women. This increased prevalence rate has not been accompanied by improved understanding about potential risks of asthma and asthma medications on pregnancy outcome or by improved knowledge about the influence of pregnancy itself on asthma symptomatology. The investigators propose to conduct a prospective study, stratified and frequency matched by race and ethnicity, of 13,000 women screened in early pregnancy. Study groups will compare 1,100 women with a prior diagnosis of asthma and 1,650 unexposed controls; providing 50% white, 30% Hispanic and 20% black study subjects. Asthmatic women will be monitored using spirometry and objective clinical criteria throughout pregnancy for symptom changes and medication use. The study will primarily estimate increased risk, owed to asthma symptoms and asthma medication (particularly bronchodilators), on preterm labor, preterm delivery, and intrauterine growth retardation. Secondary outcomes are gestational hypertension, pre eclampsia and spontaneous abortion. Known and suspected risk factors for the pregnancy outcomes and asthma will be studied to evaluate their role in the etiology of gestational asthma, to control for confounding, and assess effect modification. The asthmatic risk factors of primary interest will be evaluated at discrete points in pregnancy, permitting an analysis of their effect at different stages of pregnancy. With at least 80% power, the study will be able to detect increased risks of 2.0 in the least prevalent primary outcomes. The investigators state that this study will contribute data necessary to clarify clinical guidelines for managing asthma during pregnancy. Estimates of any elevated risk of adverse pregnancy outcome owed to asthma or asthma medication will be identified. In particular, any differences in the natural history, risks, and management of gestational asthma among white, black and Hispanic will be described.